The integration of a solar thermal system into a district heating network can be a cost-effective solution, especially for new low-energy residential areas. Because of this, many new small solar district heating systems are built at the same time as the buildings, allowing for a more holistic approach to the design and construction. In doing so, it is possible to optimise the integration of the solar thermal system with respect to both cost and technical layout. This thesis presents studies that aim to investigate the most energy efficient distribution concept for successful implementation of solar district heating technology. An existing solar assisted district heating system is modelled in simulation software and the distribution system is varied in order to find out whether there is a more energy efficient option. Three system concepts are investigated: 1. A Hybrid system using a combination of high-temperature, conventional steel pipe primary culvert, intermediate substations containing solar buffer stores and a low-temperature, EPSPEX secondary culvert with DHW-circulation (so-called GRUDIS).2. A Conventional distribution system with steel pipes, higher operating temperatures and centralized solar buffer stores.3. An All GRUDIS system, using only EPSPEX distribution with DHW-circulation, lower operating temperatures and centralized solar buffer stores.A sensitivity analysis is performed by simulating the three different distribution system for various linear heat densities, with the added objective of detecting any range-bound limitations of the different distribution systems. Results indicate that both the hybrid and All GRUDIS distribution concept is preferable to conventional DH distribution regardless of the network heat density. The hybrid concept seems preferable in denser district heating networks, but results are inconclusive regarding the best concept for sparser networks. Preliminary economic considerations show that the initial investment costs may be reduced by changing from a Hybrid to an All GRUDIS distribution concept, although a more detailed analysis is needed to draw conclusions about the most economical solution.Keywords: District heating, solar thermal, simulation, renewable energy, 4DH. / <p>Licentiate thesis; Accession Number: crp.8240e9e6.fbe5.423b.98bd.d846b0eeb3ab; Publication Type: Thesis; Language: English</p>

Anthropogenic activities are responsible for the impact of global climate change because of burning fossil fuels releasing harmful gases into the environment. As a result, the global temperature has risen about 1.18 °C since 1880, causing the global sea level to rise by 178 mm over the past century. This is a threat to countries that are closer to the ocean, especially the low-lying countries such as the Maldives. It is predicted if the sea level keeps rising, most of these islands could be below sea level by 2030. The Maldives has a tropical climate requiring cooling to achieve thermal comfort. Electricity is used to provide cooling which is generated by burning fossil fuels. Due to the need for more buildings and the effects of global warming, the demand for cooling has increased, ultimately increasing the emissions. Therefore, this paper investigated the methods to minimize the building cooling demand by creating a building model of a school in Feydhoo, Addu City, Maldives using DesignBuilder software. Also, to analyze the potential of using solar technology in providing cooling for the building, a clean energy source reducing emissions. The base model of the building showed that annual electricity consumption for cooling would be about 200.14 MWh. Based on the base model, multiple building models were created to understand the best option that can lower the cooling demand of the building. The results showed that having a super-insulated timber construction could be a better option by using improved double-glazed low-E windows and an improved cooling system with a COP of 3.2. This lowered the cooling energy demand to about 103.71 MWh. Based on these results, a solar thermal cooling system was simulated using Polysun software which shows that solar thermal collectors were not able to provide the required cooling to run the chiller system. Hence, another option was explored where DesignBuilder software was used to model a solar PV array system to provide cooling for the building. But by using a better air conditioning system (VRF system coupled with a DOAS) to provide fresh conditioned air into the building, improving the indoor air quality. The results showed that the new PV array system was able to provide the electricity required not for cooling but for other electrical requirements (total of 163.31 MWh). It also resulted in a surplus of 1 MWh of electricity exported to the utility grid, achieving a net-positive energy building.

A ground source heat pump (GSHP) system utilizes a borehole heat exchanger to extract energy from the ground during the heating season and to deposit energy during the cooling season. This requires the drilling of an extended borehole, typically ranging from 100 to 200 meters in length, with a diameter of approximately 6 to 8 inches. Inside the borehole, a U-shaped tube is placed and surrounded by a grout that aids heat transfer between the tube and the surrounding soil. A heat transfer fluid, often a mixture of water and glycol, circulates through the tube to exchange heat with the ground. During the winter, the system draws energy from the ground for household space heating, while in the summer, when air conditioning is used, it expels energy from the house into the ground. In regions with heating-dominated climates, such as Canada, more energy is withdrawn from the ground during the winter than can be naturally restored during the summer. Consequently, the soil progressively cools over time, leading to reduced heat pump coefficient of performance and a decline in the overall system efficiency. This study explores a solution to this issue by integrating solar domestic hot water systems which employ solar thermal collectors to heat water for domestic purposes. These systems are relatively straightforward, consisting of solar thermal collectors, piping, pumps, a hot water tank, and controllers. The collector area is designed to deliver high solar fractions during the summer, but it typically exhibits lower efficiency in the winter. In Toronto, annual solar fraction, defined as the proportion of energy supplied by the solar thermal system to the total energy required by the load, typically range between 50-70%. This research aims to leverage solar thermal collectors for recharging the ground during the summer months. This approach enables the installation of larger collector areas, improving system performance in the winter, while simultaneously depositing excess energy into the ground during the summer. Notably, this study focuses on a single household located in Toronto, Canada, where the recommended solar thermal collector area is 10 square meters, and the borehole heat exchanger length is 150 meters. Also, it is assumed that four people are living in this house and required energy for heating and cooling of the house are 28000 and 7000 kWh per year, respectively. This approach offers a promising solution to balance seasonal heat transfer to the ground, mitigating the long-term decline in GSHP performance. The study demonstrates that by coupling the solar thermal system with the GSHP, the targeted outcomes are achievable. / Thesis / Master of Applied Science (MASc)

The provision of a sustainable energy supply is one of the most important issues facing humanity at the current time, given the strong dependence of social and economic prosperity on the availability of affordable energy and the growing environmental concerns about its production. Solar thermal power has established itself as a viable source of renewable power, capable of generating electricity at some of the most economically attractive rates. Solar thermal power plants are based largely on conventional Rankine-cycle power generation equipment, reducing the technological risk involved in the initial investment. Nevertheless, due to the variable nature of the solar supply, this equipment is subjected to a greater range of operating conditions than would be the case in conventional systems. The necessity of maintaining the operational life of the steam-turbines places limits on the speed at which they can be started once the solar supply becomes available. However, in order to harvest as much as possible of the Sun’s energy, the turbines should be started as quickly as is possible. The limiting factor in start-up speed being the temperature of the metal within the turbines before start-up, methods have been studied to keep the turbines as warm as possible during idle-periods. A detailed model of the steam-turbines in a solar thermal power plant has been elaborated and validated against experimental data from an existing power plant. A dynamic system model of the remainder of the plant has also been developed in order to provide input to the steam-turbine model. Three modifications that could potentially maintain the internal temperature of the steam-turbines have been analysed: installation of additional insulation, increasing the temperature of the gland steam and use of external heating blankets. A combination of heat blankets and gland steam temperature increase was shown to be the most effective, with increases in electricity production of up to 3% predicted on an annual basis through increased availability of the solar power plant. / Hållbar energiförsörjning är för närvarande en av de viktigaste frågorna för mänskligheten. Socialt och ekonomiskt välstånd är starkt kopplat till rimliga energipriser och hållbar energiproduktion. Koncentrerad solenergi är nu etablerad som en tillförlitlig källa av förnybar energi och är också ett ekonomiskt attraktivt alternativ. Koncentrerade solenergikraftverk bygger till stor del på konventionella Rankine-cykel elgeneratorer, vilka minskar de tekniskt relaterade riskerna i den initiala investeringen. På grund av solstrålningens skiftande karaktär utsätts denna utrustning för mer varierade driftsförhållanden, jämfört med konventionella system. Behovet av att bibehålla den operativa livslängden på ångturbiner sätter gränser för uppstartshastigheten. För att utnyttja så mycket som möjligt av solens energi bör ångturbinen startas så snabbt som möjligt när solstrålningen blir tillgänglig. Eftersom temperaturen i metalldelar hos turbinerna är den begränsande faktorn, har metoder studerats för att hålla turbinerna så varma som möjligt under tomgångsperioder. En detaljerad modell av ångturbiner i ett solenergikraftverk har utvecklats och validerats mot experimentella data från ett befintligt kraftverk. En dynamisk systemmodell av de övriga delarna av anläggningen har också utvecklats för att ge input till ångturbinsmodellen. Tre modifieringar som potentiellt kan bidra till att upprätthålla den inre temperaturen i ångturbiner har analyserats: montering av ytterligare isolering, ökning av temperaturen hos glänsångan och användning av elvärmefiltar. En kombination av elvärmefiltar och en temperaturökning av glänsångan visade sig vara det mest effektiva alternativet. Åtgärderna resulterade i en ökad elproduktion på upp till 3%, beräknat på årsbasis genom ökad tillgänglighet hos kraftverket. / QC 20110629 / TURBOKRAFT

This thesis presents investigations on air-cooled air gap membrane distillation for desalination and the application of radial waveguides based on total internal reflection for solar thermal desalination. Using an air-cooled design for an air gap membrane distillation (AGMD) process may result in significantly lower energy requirements for desalination. Experiments were conducted on AGMD module to study the effect of air gap, support mesh conductivity and hydrophobicity, condensing surface hydrophobicity. A novel modular design was used in which modules could be used in a series configuration to increase the flux value for the distillate. The output from the series configuration was found to have about three times the production from a single pass water-cooled system with the same temperature difference between the saline and clear water streams. The results also indicated that the mesh conductivity had a favorable effect on the flux value whereas the hydrophobicity of the mesh had no significant effect. The hydrophobicity of the condensing surface was favorable on two accounts: first, it led to an increase in the flux of the distillate at temperatures below 60 °C and second, the temperature difference of the saline feed when it enters and leaves the module is lower which can lead to energy savings and higher yields when used in a series configuration. The second part of the thesis considers use of low-cost radial waveguides to collect and concentrate solar energy for use in thermal desalination processes. The optical-waveguide-based solar energy concentrators are based on total internal reflection and minimize/eliminate moving parts, tracking structures and cost. The use of optical waveguides for thermal desalination is explored using an analytical closed-form solution for the coupled optical and thermal transport of solar irradiation through a radial planar waveguide concentrator integrated with a central receiver. The analytical model is verified against and supported by computational optical ray tracing simulations. The effects of various design and operating parameters are systematically investigated on the system performance, which is quantified in terms of net thermal power delivered, aperture area required and collection efficiency. Design constraints like thermal stress, maximum continuous operation temperature and structural constraints have been considered to identify realistic waveguide configurations which are suitable for real world applications. The study provides realistic estimates for the performance achievable with radial planar waveguide concentrator-receiver configuration. In addition to this, a cost analysis has been conducted to determine the preferred design configurations that minimize the cost per unit area of the planar waveguide concentrator coupled to the receiver. Considering applications to thermal desalination which is a low temperature application, optimal design configuration of waveguide concentrator-receiver system is identified that result in the minimum levelized cost of power (LCOP). / Master of Science

Thesis (MScIng)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The Spier Estate - a wine estate in the Western Cape Province of South Africa - is engaged in a transition towards operating according to the principles of sustainable development. Besides changes in social and other environmental aspects, the company has set itself the goal to be carbon neutral by 2017. To this end, Spier is considering the on-site generation of electricity from renewable energy sources. This study was initiated to explore the technical and economic feasibility of a concentrating solar power plant for this purpose on the estate. The investigation was carried out to identify the most appropriate solar thermal energy technology and the dimensions of a system that fulfils the carbon-offset requirements of the estate. In particular, potential to offset the annual electricity consumption of the currently 5 570 MWh needed at Spier, using a concentrating solar power (CSP) system, was investigated. Due to rising utility-provided electricity prices, and the expected initial higher cost of the generated power, it is assumed that implemented efficiency measures would lead to a reduction in demand of 50% by 2017. However, sufficient suitable land was identified to allow electricity production exceeding today’s demand. The outcome of this study is the recommendation of a linear Fresnel collector field without additional heat storage and a saturated steam Rankine cycle power block with evaporative wet cooling. This decision was based on the system’s minimal impact on the sensitive environment in combination with the highest potential for local development. A simulation model was written to evaluate the plant performance, dimension and cost. The analysis was based on a literature review of prototype system behaviour and system simulations. The direct normal irradiation (DNI) data that was used is based on calibrated satellite data. The result of the study is a levelised cost of electricity (LCOE) of R2.741 per kWh, which is cost competitive to the power provided by diesel generators, but more expensive than current and predicted near-future utility rates. The system contains a 1.8 ha aperture area and a 2.0 MWe power block. Operating the plant as a research facility would provide significant potential for LCOE reduction with R2.01 per kWh or less (favourable funding conditions would allow for LCOE of R1.49 per kWh) appearing feasible, which results in cost competitiveness in comparison a photovoltaic (PV) solution. Depending on tariff development, Eskom rates are predicted to reach a similar level between 2017, the time of commissioning, and the year 2025. The downside is that the plant would not solely serve the purpose of electricity offsetting for Spier, which may result in a reduced amount of electricity that may be generated. Further studies are proposed to refine the full potential of cost reduction by local development and manufacturing as well as external funding. This includes identification of suitable technology vendors for plant construction. An EIA is required to be triggered at an early stage to compensate for its long preparation. / AFRIKAANSE OPSOMMING: Die Spier wynlandgoed in die Wes-Kaap Provinsie van Suid-Afrika is tans in ‘n oorgangsfase tot besigheids-praktyke gebaseer op volhoubare ontwikkeling. Afgesien van die sosiale en omgewingsaspekte het die groep hom ook ten doel gestel om koolstof neutraal te wees teen 2017. Ten einde hierdie doel te bereik, moet die maatskappy sy algehele elektrisiteitsverbruik vervang met hernubare bronne. Hierdie studie is dus geloods om die tegniese en ekonomiese uitvoerbaarheid van 'n gekonsentreerde sonkragstasie op die landgoed te ondersoek. Hierdie ondersoek is gedoen om die mees toepaslike sontermiese tegnologie en die grootte van 'n termiese sonkragstelsel te bepaal, wat aan die koolstof vereistes van die landgoed voldoen. Die potensiaal om die jaarlikse elektrisiteitsverbruik van 5 570 MWh met 'n gekonsentreerde elektriese sonkragstelsel te vervang, is ondersoek. Weens die toename in die elektrisiteitsprys en die verwagte hoërkoste van opgewekte elektrisiteit word aanvaar dat die implementering van voorgestelde doeltreffendheidsverbeteringe, sal lei tot 'n afname in die aanvraag na elektrisiteit van tot 50% teen die jaar 2017. Voldoende beskikbare grond is geïdentifiseer om genoeg elektrisiteit te produseer om die huidige vraag na elektrisiteit te oorskry. Die uitkoms van die studie is die aanbeveling van 'n lineêre Fresnel kollektorveld sonder addisionele warmte storing, asook 'n versadigde stoom Rankine sikluskragblok met ‘n nat-verdamping verkoelingstelsel. Die besluit is gebaseer op die stelsel se minimale impak op die omgewing, tesame met die hoogste potensiaal vir plaaslike ontwikkeling. 'n Simulasie is ontwikkel om die aanleg se werkverrigting, grootte en koste te evalueer. Die analise is gebaseer op 'n literatuuroorsig van 'n prototipe stelsel gedrag en stelsel-simulasies. Die direkte normale sonstralings data wat gebruik is, is gebaseer op gekalibreerde satelliet data. Die bevinding van die studie is 'n gebalanseerd koste van elektrisiteit van R2.74 per kWh, wat mededingend is met die koste van elektrisiteit wat deur diesel kragopwekkers verskaf word, maar is aansienlik duurder as die huidige en toekomstige voorspellings van Eskom-tariewe. Die stelsel bevat 'n 1.8 ha son kollektor oppervlakte en 'n 2.0 MWe krag-blok. Daarbenewens, sal die gebruik van die aanleg as 'n navorsingsfasiliteit die potensiaal hê om die gebalanseerd koste van elektrisiteit te verminder na R2.01 per kWh of minder (gunstig befondsing voorwaardes sal gebalanseerd koste van elektrisiteit van R1.49 per kWh tot gevolg hê), wat mededingend is met die koste van 'n fotovoltaïese alternatief. Daar word voorspel dat Eskom-tariewe dieselfde sal bly vanaf 2017, die jaar van inbedryfstelling van die aanleg, tot en met die jaar 2025. Die nadeel is dat die aanleg nie noodwendig uitsluitlik vir die opwek van elektrisiteit vir Spier gebruik sal word nie, en daarom kan dit lei tot 'n vermindering in die hoeveelheid elektrisiteit wat deur die aanleg opgewek word. Daar word voorgestel dat verdere studies onderneem word om die moontlikheid van koste-besparings vir die aanleg te ondersoek deur gebruik te maak van plaaslike ontwikkeling en vervaardiging, asook eksterne befondsing. Dit sluit die identifisering van geskikte tegnologie verskaffers vir die aanleg-kostruksie in. 'n Omgewingsimpakstudie, volgens die EIA regulasies, moet ook so gou as moontlik gedoen word aangesien dit n langsame proses is.

The annual gain of stationary solar thermal collectors can be increased by non-focusing reflectors. Such concentrators make use of diffuse irradiance. A collector’s incidence angle modifier for diffuse (diffuse-IAM) accounts for this utilization. The diffuse irra-diance varies over the collector hemisphere, which dynamically influences the diffuse-IAM. This is not considered by state-of-the-art collector models. They simply calculate with one constant IAM value for isotropic diffuse irradiance from sky and ground. This work is based on the development of a stationary, double-covered process heat flat-plate collector with a one-sided, segmented booster reflector (RefleC). This reflector approximates one branch of a compound parabolic concentrator (CPC). Optical meas-urement results of the collector components as well as raytracing results of different variants are given. The thermal and optical characterization of test samples up to 190 °C in an outdoor laboratory as well as the validation of the raytracing are discussed. A collector simulation model with varying diffuse-IAM is described. Therein, ground reflected and sky diffuse irradiance are treated separately. Sky diffuse is weighted with an anisotropic IAM, which is re-calculated in every time step. This is realized by gener-ating an anisotropic sky radiance distribution with the model of Brunger and Hooper, and by weighting the irradiance from distinct sky elements with their raytraced beam-IAM values. According to the simulations, the RefleC booster increases the annual out-put of the double-covered flat-plate in Würzburg, Germany, by 87 % at a constant inlet temperature of 120 °C and by 20 % at 40 °C. Variations of the sky diffuse-IAM of up to 25 % during one day are found. A constant, isotropic diffuse-IAM would have under-valued the gains from the booster by 40 % at 40 °C and by 20 % at 120 °C. The results indicate that the gain of all non-focusing solar collectors is undervalued when constant, isotropic diffuse-IAMs calculated from raytracing or steady-state test data are used. Process heat generation with RefleC is demonstrated in a monitored pilot plant at work-ing temperatures of up to 130 °C. The measured annual system utilization ratio is 35 %. Comparing the gains at all inlet temperatures above 80 °C, the booster increases the an-nual output of the double-covered flat-plates by 78 %. Taking all inlet temperatures, the total annual gains of RefleC are 39 % above that of the flat-plates without reflectors. A qualitative comparison of the new simulation model results to the laboratory results and monitoring data shows good agreement. It is shown that the accuracy of existing collector models can be increased with low effort by calculating separate isotropic IAMs for diffuse sky and ground reflected irradiance. The highest relevance of this work is seen for stationary collectors with very distinctive radiation acceptance.

Solar DEC (Desiccant and Evaporative Cooling) air-conditioning is a renewable technological approach to the future air-conditioning of buildings driven with solar-thermal heat. The principal acceptance of solar airconditioning has led to system prototypes mainly across Europe, however the diffusion of this innovative technology is proceeding slowly due to little field testing experience. In climates with coexisting heating demand particularly, a multivalent system approach that utilizes solar-heat not only for air-conditioning but also for hot water preparation and heating has potential as a feasible concept. However, previous research focused on systems using solar heat exclusively for the DEC-process. This research contributes to the advancement of the solar DEC-technology with multivalent use of solar thermal heat. The investigation consists of an initial detailed in-situ monitoring analysis of a system prototype operated in an industrial environment, followed by the development of optimised system concepts and a climate-specific analysis of the solar DEC-technology. The monitoring provided in-depth knowledge about the system operation, revealing the reasons for the insufficient refrigeration capacity achieved in practice. A detailed simulation model for an entire multivalent solar DEC-system including the heat sinks, DEC-system, heating and hot-water preparation was developed and a DEC-control strategy has been formulated. A new optimised control strategy for multivalent systems with simultaneous sink supply concept was devised. A sensitivity analysis was carried out to investigate the key design parameters for the dimensioning of multivalent solar DEC-systems. The research concluded that the auxiliary primary energy consumption of the optimised system was lower by one third compared to the initial system. Finally, a methodological zoning approach was developed, to systematically produce design-specific outline data for the application of the solar DEC-technology at climatically different sites.

In a proposed design for a concentrated solar power tower, sand is irradiated by solar energy and transfers its energy to another fluid stream by means of a finned tube heat exchanger. To maximize heat transfer and minimize potential damage to the heat exchanger, it is desired to have a very uniform flow through the heat exchanger. However, performing full scale flow tests can be expensive, impractical, and depending upon the specific quantities of interest, unsuitable for revealing the details of what it happening inside of the flow stream. Thus, the discrete element method has been used to simulate and study particulate flows. In this project, the flow of small glass beads through a square pyramid shaped hopper and a wedge shaped hopper were studied at the lab scale. These flows were also simulated using computers running two versions of discrete element modeling software – EDEM and LIGGGHTS. The simulated results were compared against the lab scale flows and against each other. They show that, in general, the discrete element method can be used to simulate lab scale particulate flows as long as certain material properties are well known, especially the friction properties of the material. The potential for increasing the accuracy of the simulations, such as using better material property data, non-uniform particle size distributions, and non-spherical particle shapes, as well as simulating heat transfer within a granular flow are also discussed.

This study describes a simulation-based approach for informing the incorporation of Phase Change Materials (PCMs) in buildings designed to the "Passive House" standard. PCMs provide a minimally invasive method of adding thermal mass to a building, thus mitigating overheating events. Phase change transition temperature, quantity, and location of PCM were all considered while incrementally adding PCM to Passive House simulation models in multiple climate zones across the United States. Whole building energy simulations were performed using EnergyPlus from the US Department of Energy. A prototypical Passive House with a 1500 Watt electric heater and no mechanical cooling was modeled. The effectiveness of the PCM was determined by comparing the zone-hours and zone-degree-hours outside the ASHRAE defined comfort zone for all PCM cases against a control simulation without PCM. Results show that adding PCM to Passive Houses can significantly increase thermal comfort so long as the house is in a dry or marine climate. The addition of PCM in moist climates will not significantly increase occupant comfort because the majority of discomfort in these climates arises due to latent load. For dry or marine climates, PCM has the most significant impact in climates with lower cooling degree-days, reducing by 93% the number of zone-hours outside of thermal comfort and by 98% the number of zone-degree-hours uncomfortable in Portland, Oregon. However, the application of PCM is not as well suited for very hot climates because the PCM becomes overcharged. Only single digit reductions in discomfort were realized when modeling PCM in a Passive House in Phoenix, Arizona. It was found that regardless of the climate PCM should be placed in the top floor, focusing on zones with large southern glazing areas. Also, selecting PCM with a melt temperature of 25°C resulted in the most significant increases in thermal comfort for the majority of climates studied.